Which of the following is/are the main advantage of using a dumpy level in surveying? i) Simple to use ii) Provides accurate level of reading iii) Can be used at night, without light
- AOnly i
- BOnly ii
- CBoth i and iiCorrect
- DOnly iii
Solution
Concept
A dumpy level is simple to use and gives accurate levelling readings, but it needs light to read the staff.
Step-by-step solution
1. Statement i: A dumpy level has a fixed telescope and few adjustments, so it is simple to use. True. 2. Statement ii: Once set up, its line of sight stays horizontal and gives accurate staff readings. True. 3. Statement iii: The staff must be seen through the telescope, so it cannot be used at night without light. False. 4. So only i and ii are correct. Answer is (C).
Explanation
A dumpy level has a telescope rigidly fixed to the vertical spindle. Its adjustments stay stable for a long time, so it is simple to use and gives accurate readings. It is an optical instrument, so it needs light to read the staff.
Why the other options are wrong
(A) Leaves out accuracy, which is a main advantage. (B) Leaves out simple use, which is also an advantage. (D) An optical level cannot read the staff in darkness, so iii is false.
Shortcut
Any optical instrument needs light, so remove every option that contains iii.
Common mistake
Thinking a level works in the dark like some electronic instruments.
Correct answer: C) Both i and ii